One of the major problems in development and aging is that we do not understand the nature of the "developmental program" through which cells and organisms pass between birth and death. Insect metamorphosis involves a developmental program with many advantages for analysis. We are investigating the hormonal control of insect metamorphosis by following cuticular protein synthesis in vitro in both short term and long term cultures. The roles of ecdysterone and juvenile hormone in controlling the switch between pupal and adult synthesis in imaginal discs which are committed to metamorphosis are being studied. Also under analysis is the relation between cellular proliferation and such differentiation. The enzymatic function of individual cuticular proteins is also being determined.